Was it possible in the last version of the board? I actually did not know that you could disable viewing avatars. I looked around and have not found anything. You can disable signatures on a per-person basis now. They should have the same feature for avatars, but it looks like they don't.
Quote from a Sooner board: "5 Big 12 teams not picked up for TV....Nebraska leaving already paying off. Their game with UT Chatty picked on the Big 10 Network."